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GSB INTERNATIONAL e.V.
Qualitätsgemeinschaft
für die Stückbeschichtung
von Bauteilen
Vereinsregister VR 10645
Düsseldorf
ID-NR. DE 152599832
Deutsche Bank Düsseldorf
BLZ 300 700 10
Konto Nr. 46 77 043
Swift Code: DEUTDEDD
IBAN: DE96300700100467704300
GSB INTERNATIONAL Am Bonneshof 5, D-40474 Düsseldorf Consultation Number 0032-5 Surface treatment (except passivation of tin-plated steel (ETP)) for applications in various industry sectors namely architectural, automotive, metal manufacturing and finishing, and general engineering (unrelated to Functional chrome plating or Functional chrome plating with decorative character) Dear Ladies and Gentlemen,
Please find attached the documentation “Chromium-free Surface Pretreatment for Aluminium, State Of The Art, GSB International, 2012” which is mentioned in 0032-5 “Analysis of Alternatives”.
The documentation describes the development and state of the art of surface pretreatment processes in the field of piecework coating of aluminium in architecture. Today there are GSB approved and sufficient processes available that are of equivalent quality and competitive to chromium-VI-containing processes. This processes passed the GSB test and approval regime with the highest standards in the market as mentioned in 0032-5 “Analysis of Alternatives”.
Today for steel and galvanized steel there are no GSB-approved chromium-free process as pretreatment before coating available. Some projects are running to develop chromium-free processes which are comparable to chromium-VI-containing processes.
If you have any question please do not hesitate to contact me.
Kind regards
Werner Mader
Attachment
Chromium-free Surface Pretreatment for Aluminium, State Of The Art, GSB International, 2012
GSB INTERNATIONAL Am Bonneshof 5 D-40474 Düsseldorf Telefon +49 (0) 211/4796 - 451 Telefax +49 (0) 211/4796 - 410 www.gsb-international.de [email protected] Geschäftsführung: Werner Mader 07.10.2015
Chromium-free
Surface Pretreatment For Aluminium State Of The Art
1
Chromium-free surface pretreatment of aluminium Documentation of the prior art
Preface
In the early 1990s, the State of Berlin issued the ban on the use of aluminium as a building material, against which the General Association of the Aluminium Industry (GDA) filed a successful opposition. However, this was associated with the requirement that chromium-free processes must be used in future for the surface pretreatment.
GSB International has faced this challenge for more than 15 years, and has worked extensively on the introduction and approval of chromium-free pretreatment processes. In close co-operation with pretreatment chemical manufacturers and coating companies, approval procedures for alternative systems were developed and then implemented in the quality guidelines. Only in 1994 was approval granted for a chromium-free pretreatment process to ensure that member companies could continue to serve their markets with alternative processes with a high quality level. Therefore, since that time, proven chromium-free pretreatment processes have become available that behave in a stable way under production conditions, have shown high corrosion resistance in long-term weathering tests and are commercially competitive.
Since its foundation over 30 years ago, GSB International has pursued a consistent strategy of developing quality-assured products, with due consideration of environmentally friendly technologies and procedures. The selection of the processes and operating sequences remains exclusively within the corporate responsibility of each individual member company. As in the past, GSB International does not specify any requirements in the quality standards that exceed the regulatory framework.
At the end of 2010, the ECHA placed chromium (VI) oxide and other chromium (VI)-containing compounds on the list of substances of very high concern (SVHC list) because they are carcinogenic and mutagenic. This raises the very important question of the future of chromating as a pretreatment process for aluminium in construction. Nevertheless, this problem has been known since the 1990s in the industrial sectors in question.
Our organisation therefore acted in a timely manner to find alternative chromium-free pretreatment processes.
The present documentation describes the development and state of the art of surface pretreatment processes in the field of piecework coating of aluminium in architecture. It also provides an insight into other markets and processes, such as coil coating, which are affected by similar legal regulations.
Düsseldorf, July 2012
Hans-Jürgen Alfort
Chairman of the Board
2
Contents
Chromium-free surface pretreatment of aluminium 1 1 Introduction 5 1.1 Current situation 5 1.2 Health endangerment 6
2 Statutory provisions 7 2.1 Architecture and construction 7 2.2 Other markets 8
3 GSB International 9 3.1 General information 9 3.2 State of the art at the time of the foundation of GSB International in 1976 9 3.3 Certification procedures of GSB International 9 3.4 Expanded certification criteria 11 3.5 Extension of natural weathering 12 3.6 Certified systems 14
4 The current development status of chromium-free processes from the perspective of the chemical manufacturers 16
4.1 Alufinish GmbH & Co. KG, D-Andernach 17 4.2 Chemetall GmbH, D-Frankfurt am Main 21 4.3 Henkel KGaA, D-Düsseldorf 26 4.4 MacDermid GmbH, D-Forst 28 4.5 Nabu-Oberflächentechnik GmbH, D-Stulln-Nabburg 29 4.6 SurTec International GmbH, D-Bensheim 33
5 The current development status of chromium-free processes from the perspective of the coaters 34
5.1 General information 34 5.2 Alulux Beckhoff GmbH & Co., D-Verl 35 5.3 Alumil-Milonas Aluminium Industry S.A., GR-Kilkis 36 5.4 heroal – Aluminiumgesellschaft Hövelhof mbH & Co. KG, D-Verl 40 5.5 LOV-Limbacher Oberflächenveredelung GmbH, D-Limbach-Oberfrohna 41 5.6 TK-Oberfläche GmbH, D-Bielefeld
and PBS Schreiner GmbH & Co. KG, D-Grebenau 46 5.7 Warema Renkhoff SE, D-Marktheidenfeld 52
3
6 Chromium-free pretreatment for coil coating 55 6.1 Hydro Aluminium Rolled Products GmbH, D-Grevenbroich and
Novelis Deutschland GmbH, D-Göttingen 55
7 Preanodisation 65 8 Summary 67
The contributions in Chapters 4, 5 and 6 represent the opinions and experience of the company. The content is solely the responsibility of the company.
4
5
1 Introduction
1.1 Current situation
On 01.06.2007, the REACH regulation came into force to replace the existing chemicals legislation in
the European Union (EU).
The REACH regulation has established a certification procedure for substances of very high concern.
As of 30.06.2011, there are 53 substances included on the candidate list (SVHC list) for certification.
The objective of the EU Commission is to expand the list to 136 substances by the end of 2013.
Publication in the "candidate list" does not result in mandatory certification but rather far-reaching
information requirements in the supply chain. REACH requires companies to inform their business
customers if their products contain more than 0.1 per cent of a chemical identified in the list.
At the end of 2010, the European Chemicals Agency (ECHA) added chromium (VI) oxide and other
chromium (VI) compounds to the candidate list for substances of very high concern (SVHC list).
The list of substances subject to mandatory certification now contains 6 substances, for which the
companies concerned must submit certification applications by 2013. The inclusion process is
currently under way for a further 13 substances. This also applies to chromium (VI) oxide, chromic
acid and other chromium (VI) compounds. After inclusion in Annex XIV of the REACH regulation, a
certification must be applied for prior to each use. The EU Commission makes the decision regarding
the certification.
The possible consequences are:
chromate-containing surface pretreatment processes may continue to be used. The required
registration of the chemicals with the ECHA is very expensive, which may lead to an increase
in the process costs.
relocation of production to non-REACH countries. The importation of chromate-containing
products without registration with the ECHA is prohibited. Here also, the required registration
can lead to price increases.
The use of chromate-containing surface pretreatment processes is prohibited without
exception.
According to current knowledge, a final decision by the European Commission is anticipated within the
next 5 years.
6
1.2 Health endangerment
Toxicological significance is ascribed to chromium (VI) compounds, which have the potential to cause
cancer. Their classification as compounds with carcinogenic and mutagenic potential has been known
for many years.
Metallic chromium and trivalent chromium compounds, such as the chromium (III)-phosphate that
makes up the green chromating layer, are not irritant, mutagenic or carcinogenic. However, the
production of process chemicals always starts from chromium (VI) compounds. Thus, the handling of
hazardous chemicals is assumed here, and particular caution is required.
Chromium (III) compounds are not included in the SVHC list, and therefore can still be used without
restriction.
7
2 Statutory provisions
2.1 Architecture and construction
The relevant national building codes and rules do not currently prohibit the use of chromium-
containing surface pretreatments.
However, individual cities and districts have switched over in their tenders to the mandatory
prescription of chromium-free pretreatments.
As early as 1990, the Building/Living Senate in Berlin, in the 40th Official Journal, prohibited the use of
building materials posing a high health and environmental hazard, and thus banned the use of window
and door profiles made of aluminium. At the meeting of 19.02.1998 (document 13/2002) in the context
of the lifting of the restriction on the use of aluminium in the regulatory area of public sector and
publicly funded construction, the Berlin Senate declared that aluminium is only allowed if
a pledge of commitment by the manufacturer for product-related recycling and
a declaration by the contractor on the chromium-free primer for coloured aluminium
components exist.
There is therefore no differentiation between chromium (VI) and chromium (III) compounds, but the
use of chromium is generally prohibited.
The decision of the Berlin Senate had a nationwide impact and so other cities, such as Munich, also
introduced the same or similar regulations.
The certification systems for sustainable construction (LEED, DGNB, etc.) also provide, in their
evaluation rules for building, positive points for the use of chromium-free surface pretreatment
processes for aluminium. For this reason, architects are increasingly inviting tenders for chromium-free
surface pretreatments.
Other European countries, like Spain, France and Greece, already have a market share of more than
60% made up of chromium-free pretreatments. In 2011, China enacted a ban on the use of chromium
(VI)-containing pretreatments in architecture.
8
2.2 Other markets
Other markets have already gone one step further here. By virtue of the Directive on End-of Life
Vehicles (2000/53/EC, 1 July 2003/1 July 2007), the use of Cr (VI)-containing compounds has long
been prohibited. Some car manufacturers have generally rejected chromium-containing compounds in
pretreatments and in the processes for surface pretreatment of aluminium.
The same applies to electrical appliances. Here the guidelines
ROHS (EU Directive 2002/95/EC on Restriction Of The Use Of Certain Hazardous
Substances In Electrical And Electronic Equipment, 1 July 2006) and
WEEE (EU Directive 2002/96/EC on Waste Electrical And Electronic Equipment, 1 July 2006)
should be highlighted.
Even in the aerospace industry, chromic acid anodisation is being replaced by tartaric acid
anodisation. New projects are generally only tendered for with tartaric acid anodisation.
9
3 GSB International
3.1 General information
These developments prompted GSB International to test chromium-free pretreatment processes in
observance of the high and proven quality standards and to incorporate them into the quality
standards as a GSB International-compatible pretreatment.
3.2 State of the art at the time of the foundation of GSB International in 1976
For more than 50 years, in the pretreatment of aluminium, chromating has performed the tasks of
improving adhesion for subsequent coating and serving as a barrier layer against substances diffusing
through any organic layer, such as water vapour or corrosive atmospheric gases. This applies to
coating with liquid and powder coats.
We primarily differentiate between yellow and green chromating. Whereas the yellow chromatic layer,
which primarily consists of chromium oxide (Cr203), still contains Cr(VI) ions, no chromium (VI) ions
can be detected any more in the green chromating layer, which primarily consists of chromium
phosphate (Cr(III)PO4). Chromium-containing conversion layers created both in the dipping and
spraying processes deliver comparably good results in relation to adhesion promotion and corrosion
inhibition. In all chromating processes, thorough rinsing to remove the adhering treatment solution is
necessary. This requires the preparation of chromate-containing rinse water to prevent chromate from
entering the waste water.
3.3 Certification procedures of GSB International
In addition to inhibiting corrosion and improving paint adhesion, for all certified and used paint
systems, the equipment suitability, processing properties and process stability of the pretreatment
process are particularly important.
This led the Technical Committee (TC) of GSB International, in developing a certification process for
alternative, chromium-free pretreatment chemicals, to propose a multi-stage sequence:
10
- Stage 1:
Application of the chemical suppliers to GSB International for certification of the relevant
pretreatment system.
Presentation of the system and discussion with the Technical Committee (TC)
For this purpose, the following documents must be prepared:
Presentation of individual results based on GSB QR AL 631
Submission of tested sample sheets
Submission of current product data sheets and material safety data sheets
Names of reference objects, if applicable
Evidence of product suitability for dipping plants and/or spraying equipment
Evidence of product suitability for powder and/or liquid coats
Plant experience
- Stage 2:
The pretreatment, coating and testing according to GSB QR AL 631 of the sample plates is
performed in a test institute to be named by the TC.
As a reference, a commercial yellow chromating has been used so far. A chromium-free "master
process" is being tested. The samples pretreated with the reference material are coated and
tested the same way.
As a reference material, a reference powder coat determined by the TC is used. The tests and
requirements are summarised in section 8.2.6 of GSB QR AL 631.
- Stage 3:
If the results of stage 2 are positive, a plant test is performed at a coating company that is a
member of GSB International.
Stage 3 must be performed in a production plant; here, the material must be pretreated with a
surface area of at least 500 m². 25 m² from the middle and end of the pretreatment lot respectively
must be coated and exposed as an object of natural weathering.
The consent of the TC for the coating company and the object is required.
The documentation of the plant test is created by an observer appointed by the TC.
11
After a positive evaluation of the results of field tests in accordance with section 8.2.6 of GSB QR
AL 631, the preliminary certification for the pretreatment system is granted.
Only the findings from the field tests confirm the plant suitability and process stability of the
alternative treatment processes.
- Stage 4:
Sample material from the pilot test (stage 3) is weathered for three years in a near-shore industrial
climate (preferably in Hoek van Holland in the Netherlands). Once the natural weathering results
have been obtained, if the progression is positive, the final certification may be granted and
authenticated for the pretreatment system.
- Extension test
The certified alternative pretreatment chemicals, like the coating materials, are subject to an
annual extension test. The test samples required for the extension test, in the form of ready-
coated profiles or sheets, are removed by the tester from a coater who is routinely using the
pretreatment chemical to be tested. In the event of positive test results, the certification is
extended by one year.
3.4 Expanded certification criteria
For alternative pretreatment processes, increased care in degreasing, pickling and rinsing with
completely desalinated water (DW) prior to the conversion treatment is crucial. The quality of the
product "coated material" is essentially dependent on the pretreatment, the coating material and the
careful application of the coating. Therefore, in the currently valid quality guidelines, expanded
certification criteria have been included.
Thus, in 2007, GSB International introduced the status of "premium coater". The most important
quality criterion for the premium coater is the precise definition of the pretreatment process with
product testing.
12
Here, for the first time in a quality community, the entire pretreatment process is documented, stored
and monitored by means of corrosion tests on coated products. Process changes must always be
communicated. Another aspect is the increased documentation of self-monitoring for the premium
coater.
With the premium segment for the coater and the coating material, there is increased security for the
life expectancy of constructed façade sections. For the first time, the detailed definition and monitoring
ensures additional security, which is not the case with national and international standards.
3.5 Extension of natural weathering
Since the beginning of the natural weathering tests in Hoek van Holland, GSB International did not
end the exposure after three years, but extended the test period to ten years. The samples removed
after ten years were documented and handed over to the respective pretreatment manufacturers for
storage.
Examples after ten years of natural weathering in Hoek van Holland, with chromium-free pretreatment
processes:
Image: Alodine 4830 (Henkel), exposure 1999
Image: Alfipas 745 (Alufinish), exposure 1998
13
Image: Alficoat 748 (Alufinish), exposure 2001
Image: Nabutan STI 310 (Nabu), exposure 1998
Image: X4707 (Chemetall), exposure 1999
14
3.6 Certified systems
Alternative pretreatment systems, chromium-free (Rinse and No-Rinse)
Company Internet System
Certification Henkel KGaA www.henkel-
technologies.de Alodine 4830/31
(powder coating area) Stage 4
Alodine 400 Stage 4
NABU-
Oberflächentechnik GmbH
www.nabu-stulln.de Nabutan STI / 310 (powder coating area)
Stage 4
Nabutan 900 Stage 2
Alufinish GmbH &
Co. KG www.alufinish.de Alfipas 745/746 (powder
coating area) Stage 4
Alficoat 748 (powder coating area)
Stage 4
Alfipas 7816 Stage 3
Chemetall GmbH www.chemetall.com Gardobond X 4707 Stage 4
Oxsilan AL 0510 Stage 3
Chemische Werke Kluthe
www.kluthe.com Deccordal Al230A Stage 4
CHEMAL GmbH &
Co. KG www.chemal.com Non-Chrome B.K.-3990 Stage 4
MacDermid GmbH www.macdermid.com Iridite CF (powder
coating area)Stage 4
AD Chemicals B.V. www.adinternational.com Precoat Cr-free (powder
coating area)Stage 3
Surf Chem – Skylodimos
Bros.
SurfPass Ti NOC Powder coating area
Stage 3
15
Alternative pretreatment systems, chromate-free (Rinse and No-Rinse)
Company Internet System
Certification
Henkel KGaA www.henkel-technologies.de
Alodine 5992 Stage 3
SurTec International
GmbH www.surtec.com SurTec ChromitAl
650 TCP(powder coating area)
Stage 3
16
4 The current development status of chromium-free processes from the perspective of the
chemical manufacturers
The following contributions reflect the opinions and experiences of the companies. The
content is solely the responsibility of the chemical manufacturers.
Schematic representation of the different surface pretreatment processes
17
4.1 Alufinish GmbH & Co. KG, D-Andernach
4.1.1 Alfipas 745 - Alfipas 746 (ENVIROX S - process)
This system is a two-component system for the pretreatment of aluminium surfaces, consisting of the
Alfipas 745 (titanium-containing component) and the polymer component Alfipas 746. Both
components are liquid and therefore automatically dosed. Alfipas 745 - Alfipas 746 can both be
applied in dipping as well as spraying processes, and then rinsed, as is usual in chromating
processes. The preparation is performed in fully desalinated water. The layer is about 30 nm thick; the
ideal titanium layer application is 2 - 10 mg Ti/m².
The conversion coating produced is colourless and can be easily made visible by a dye spot test
(quick test). The precise titanium layer application is determined quantitatively by the photometric layer
determination method. In addition, detection with X-ray fluorescence analysis is possible.
Alfipas 745 and 746 received the final GSB International certification already in January 2002. The 10-
year natural weathering in Hoek van Holland (NL) by GSB International was completed successfully in
January 2009.
Alfipas 745 and 746 is currently used in 5 countries - Germany, Belgium, Hungary, Greece and the
Czech Republic - in the fields of architecture, medical equipment, household appliances and
machinery.
Image: Company facade of ALUCOLOR Oberflächenveredlung GmbH & Co. KG, D-Chemnitz
Implementation: March 1998, area 1059 m²
18
4.1.2 Alficoat 748 (ENVIROX NR process)
Alficoat 748 is a 1-component product based on titanium and polymer compounds for the pretreatment
of aluminium surfaces. It is liquid, may be automatically dosed, and can be applied both in dipping and
spraying processes.
Since this is a no-rinse product, a final rinse is not required. The preparation is performed in fully
desalinated water.
The layer is about 30 nm thick; the ideal titanium layer application is 2 - 10 mg Ti/m². Also available as
detection methods are the quick test, photometric determination and X-ray fluorescence analysis. The
10-year natural weathering in Hoek van Holland (NL), according to information from the FEM Institute
in Schwäbisch Gmünd, was successful, and an official letter from GSB International is expected in late
November.
Alficoat 748 is already used in machine engineering and architecture in 16 European and Eastern
European countries, as well as in the Middle East.
Image: Production of 55 m² façade panels for the operations building of Zuck Mechanik GmbH,
D-Ochtendung, execution: May 2001
19
4.1.3 Experiences and special features of Alficoat 748 and Alfipas 745 - Alfipas 746
Chromium-free systems are more sensitive than chromating. Therefore, a good rinsing technique, in
particular prior to the chromium-free pretreatment, is required (dripping water at maximum 30 μS/cm)
in order to reduce the entry of pollutants. In addition to determining the concentration, the
measurement of the pH and conductivity, Alfipas 745 - Alfipas 746 and Alficoat 748 baths are
determined via the V-value. This includes the degree of contamination. Thus it can be easily
determined when a bath should be renewed (similar to chromium (III) determination with chromating).
For turbid baths, a simple filtration process is also available (Envirox cartridge filter system), which can
eliminate harmful precipitates. In continuously operating plants with high throughput, the bath should
constantly be partially renewed to keep the entry of contaminants or degradation products to a
(harmless) level. We also recommend that, for large goods throughput and the use of Alficoat 748,
after-misting of the chromium-free treated surfaces with fully desalinated water (low water quantity) be
performed to remove any product residues from the drip rail. A trouble-free application is possible if
these points and the specified operating parameters are considered.
4.1.4 Alfipas 7816 (ENVIROX SG process)
The ENVIROX SG process is the latest development of our chromium-free pretreatment processes.
Alfipas 7816 is a 1-component product and contains zirconium- and polymer-containing compounds. It
is a sol-gel system that is suitable for the pretreatment of various metal surfaces (aluminium alloys,
steel and galvanised surfaces). It is liquid and can therefore be automatically dosed. The preparation
is in fully desalinated water, and a brief rinse in the same water is also required. It can be applied both
in dipping and spraying processes.
The layer thickness is in the nanometre range.
The conversion coating produced is colourless on aluminium and galvanised surfaces; on steel
surfaces, however, it appears yellowish-brown.
The same may easily be made visible by the dye spot test (quick test). The precise layer application
(expressed in extinction values) is determined quantitatively by the photometric layer determination
method.
20
Stage 2 of the GSB International certification procedure was completed successfully. An official
statement by GSB International will be available shortly.
Alfipas 7816 is currently being used in 9 European and Eastern European countries, as well as in the
Middle East, for the pretreatment of office furniture (steel), and galvanised fences, as well as other
custom coatings of aluminium and steel.
21
4.2 Chemetall GmbH, D-Frankfurt am Main
4.2.1 Chromium-free alternatives for every application
Nearly 40 million tons of aluminium are manufactured worldwide each year. The main customers
include the construction and automotive industries, as well as the mechanical and plant engineering.
Due to its chemical properties, like many other metals, aluminium must be protected by pretreatment
against environmental influences. In addition to corrosion protection, these measures are also used to
ensure better paint adhesion. The chromium-free alternatives described below have proven
themselves over many years of use, and are characterised by particular application-specific strengths:
Gardobond® X 4707 (titanium- / zirconium-containing process)
Gardobond® X 4661 (Self Assembling Molecules (SAM) process)
Permatreat® 1903 (aluminium pretreatment process)
OXSILAN® (silane-based process)
4.2.2 Impeccable façades even after 15 years
Glass, concrete and aluminium now determine the image of modern architecture. Above all, doors,
windows, window sills and entire façade panels are made of flexible lightweight material aluminium.
Because heat, sun and salty or polluted air place extreme demands on corrosion protection, all
products are pretreated and then either powder-coated or painted. Chromium-free Gardobond® X
products have proven themselves in this market for over a decade. Since then, in the building industry
alone, many millions of square metres of aluminium have been coated with Gardobond® X processes!
Qualitative or visual impairments cannot be observed, even over the long term. Façade panels from
the world's leading manufacturer A&MS also show no signs of ageing for years. Today, the second,
more advanced generation is already in use under the name Gardobond® X 4707. This technology,
based on titanium and zirconium, shows excellent results in all of the usual test processes (NSS,
CASS or filiform). Even under the most difficult conditions, such as the ten-year GSB International
"Natural Weathering Test" (Hoek van Holland, Netherlands), aluminium samples prepared with
Gardobond® X 4707 outperformed chromated pendants. In addition to GSB International certification,
Gardobond® X 4707 is certified by Qualicoat and meets the AAMA requirements.
22
4.2.3 Other fully certified alternatives
With the silane-based Oxsilan® AL 0510, Chemetall offers another chromium-free alternative that also
has all the necessary certifications for the construction industry (GSB International, Qualicoat).
Specially developed for the pretreatment of aluminium-containing alloys and other metals, the
environmentally friendly OXSILAN® process has been successfully used for many years in the
household appliance and automotive industries (see below). Both aluminium pretreatment processes
are characterised by a simple process control and can also be used in spraying, dipping or cascade
processes. The baths of the stable, low-sensitivity processes are easy to control online and are
characterised by low maintenance requirements. With simple "quick tests", all alternative chromium-
free coatings from Chemetall can be determined both by XRF (X-ray fluorescence analysis) and with
qualitative and quantitative methods.
4.2.4 Perfect surfaces with Gardobond® X 4661
If, in addition to high corrosion, high optical performance is also required, then many conventional
processes show their limitations. An example is the sheened and polished surfaces of alloy wheels. In
this area, the chromium-free Gardobond® X 4661 process, also known as the SAM process, shows
the best properties, because it has optically neutral behaviour towards the surface. Even on profile
material used for furniture, shower enclosures, vehicle accessories and in architecture, the SAM
treatment shows very good test results. The abbreviation SAM stands for Self-Assembling Molecules.
At the microscopic level, the SAM molecules form a homogeneous, monomolecular film on the
metallic surface, which leads to a very good corrosion protection and ensures excellent paint
adhesion. Since the chemical reaction takes place in a few seconds, very high production rates can be
achieved, which increase plant productivity. Chemetall is a leading supplier of chromium-free
pretreatment processes for aluminium wheels, with more than 60 customers worldwide.
In addition, the SAM process can be used, depending on the application area, usually without
significant plant-specific adaptations. The process sequence and the number of baths do not generally
change. The process is very robust; the checking may be performed by means of electrical
conductivity and pH value. SAM levels can also be directly determined with a photometer.
23
4.2.5 Permatreat® 1903 for the food industry
Since the turn of the millennium, many food and beverage and can makers have switched to another
chromium-free alternative from Chemetall: Permatreat® 1903. Excellent properties in terms of
corrosion protection and adhesion and compatibility with a variety of different paint systems make this
a very flexible and attractive process. The quality of the coating surpasses to some extent the level of
the chromium (III)-containing predecessor. Both in the conventional dipping process and in the no-
rinse process, the can lids that require increased corrosion resistance, can be pretreated. Permatreat®
1903 is certified by the Nehring Institute (testing of elution) as well as by many leading can
manufacturers such as Ball, Impress and Crown, to name just a few. With only minor modifications,
Permatreat® 1903 can be used in all conventional food and beverage canning lines.
4.2.6 A true multimetal-ready alternative
Looking beyond aluminium pretreatment, multimetal capability is today becoming increasingly
important. In the automotive industry, the growing material mix in the bodywork and components
demands greater flexibility; in the electronics, the electrical current flows in ever finer and narrower
tracks, and all materials are continuously exposed to higher stresses. Process-related disadvantages
of phosphating, such as hydrogen evolution, which can lead to material embrittlement or the increase
in electrical resistance in the blank corrosion protection, are therefore more and more difficult to
overcome. In this context, the silane-based OXSILAN®technology has proven itself to be technically
superior:
Oxsilan® is multimetal-readyall
common metals and alloys can be treated (steel, cast steel, galvanised steel, aluminium,
magnesium, etc.)
Oxsilan® is environmentally friendly
- No hazardous heavy metals such as nickel
- Low water consumption (multiple use of rinse water is possible)
- Virtually no sludge production
- Very low waste disposal costs
- Simple wastewater treatment
24
High economic efficiency
- Sparing on material requirements (thin layers)
- Energy-saving (room temperature)
- Fewer process steps (no activation or passivation steps, rinsing steps may be
omitted in some cases)
- - Low disposal costs (no heavy metals)
Short treatment times (increased productivity)
Simple and robust chemistry, stable process
For job coaters, the multimetal capability plays an important role. Motor housing made from aluminium,
steel axle parts, roof rails made from stainless steel or magnesium-containing instrument panel
supports must pass through the pretreatment baths in the shortest possible cycle times. This change
represents a major challenge to phosphating. With OXSILAN®, all common metals in the automotive
industry and in the E/E and construction industry, such as steel, stainless steel, aluminium or
magnesium alloys and cast steel, can be pretreated. Another major advantage of this silane-based
technology proves to be the lot operation mode. This allows pure aluminium components to be
implemented over a longer period. Chemetall offers job coaters who want to completely dispense with
a bath exchange, depending on the required quality level, an OXSILAN® system that can pretreat the
entire variety of substrates in a single bath.
More than 300 companies, of which 50 are in the automotive industry, today use OXSILAN®
worldwide. Since 2009, this new thin-film technology is used increasingly in bodywork pretreatment.
Meanwhile Daimler, Opel, PSA, Renault and Hyundai in various plants have converted their
component or bodywork pretreatment to OXSILAN®. Compromises in terms of process reliability,
quality, durability, delivery punctuality or costs are unacceptable in this highly competitive market. The
fact that this process has still been able to prevail across the board speaks volumes. Finally, practice
has shown that the conversion is economically worthwhile. A comparison of relative costs calculated
from average values illustrates this. The sometimes dramatically lower costs for energy and waste
disposal should have an even stronger effect in the coming years, because even optimists are not
anticipating lower prices in this area.
25
Zinc phosphating OXSILAN® process
Heating costs 100 60
Electrical energy 100 70
Rinsing water 100 30
Waste removal 100 15
Maintenance costs 100 20
Table: Comparison of relative costs (average values)
The switch to the chromium-free OXSILAN® process often reduces costs. The sometimes dramatically
lower costs for energy and waste disposal should have an even stronger effect in the coming years.
4.2.7 Conclusion & outlook
It is understandable and legitimate that user of chromium technologies will attempt to obtain an
extension of the grace period. Objectively, however, there is no doubt that this transitional period will
have a tendency to come to an end. Other niches in the industrial use of chromium are also likely to
disappear gradually. Fortunately, optimally functional replacement technologies have long been
established, which neither in quality nor in costs or availability are inferior to the chromium-containing
process. The opposite is much more often the case: The conversion is often achieved quickly, easily
and without significant costs. There are also attractive savings, because all of the presented
alternative technologies offer a simpler and more stable processes and lower energy consumption.
Since all processes are free of heavy metals, the costs of waste water and refuse treatment are also
reduced. Persisting with the outdated and harmful technology is perhaps understandable, but this
position is not rational.
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4.3 Henkel KGaA, D-Düsseldorf
Modern alloy coatings are highly specialised processes that must meet a wide variety of different
requirements. Along with high-performance corrosion protection, for metal processing companies the
use of environmentally friendly production processes increasingly plays an important role. As a
specialist in surface coatings, Henkel, with its broad product portfolio, sets industry-wide standards.
Under the Alodine brand, the company presented, at the ALUMINIUM 2010 fair, sustainable coating
technologies that combine the highest quality with responsibility towards people and the environment.
At ALUMINIUM 2010, Henkel was represented as a technology leader in the field of surface
pretreatment with its own stand. Under the slogan "One Source For All Needs - Alles aus einer Hand",
the company presented itself as a competent partner that, under the Alodine brand, offers innovative
technologies for pretreatment of aluminium prior to painting. These are equal to the constantly
changing demands of the aluminium industry and ensure maximum corrosion protection with minimal
environmental impact.
4.3.1 Alodine 400 - Chromium-free coating without sacrificing quality
With its chromium-free Alodine 400 process, for example, Henkel presents a process for the
pretreatment of aluminium surfaces that will not only improve environmental performance and
occupational health and safety, but also fulfils the high quality requirements in terms of paint adhesion
and corrosion resistance of powder coated materials. The use of this technology, which is exempt
from labelling requirements, offers businesses the advantage of being able to completely dispense
with conventional wastewater treatment, since the process does not involve any heavy metals. At the
same time, the plant operator also benefits from improved employee safety.
Practical experience confirms the high quality of the chromium-free process. Thus, on the metallic
surface, a transparent titanium-based conversion coating is generated that durably protects the
powder-coated parts provides against corrosion and, as an adhesion substrate, improves the
subsequent paint application. The modern conversion process of Alodine 400 has GSB International
and Qualicoat certification, thus offering ideal conditions for a long-term weather-resistant powder
coating.
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4.3.2 Alodine 5992 - corrosion protection for unpainted surfaces
Another new development in the field of metal pretreatment is Alodine 5992. In contrast to toxic
chromium (VI)-containing passivations, the conversion coating produced by this process is based on
non-toxic chromium (III) compounds. In view of the many regulatory requirements, such as the ROHS,
WEEE and ELV directives, Alodine 5992 represents a real alternative to traditional conversion
treatments. The trivalent layer of an equivalent blank metal corrosion resistance for unpainted
aluminium surfaces, as well as an optimal adhesion substrate for application of paint; the powder-
coated aluminium parts have the same corrosion protection as yellow chromated sheets and profiles.
Alodine 5992 is Qualicoat certified and also meets the MIL requirements for use in the aerospace
industry. Moreover, the use of the process facilitates wastewater treatment and disposal, since the
reduction of hexavalent chromium to the trivalent form is not necessary.
Under the Alodine brand, Henkel is developing modern and sustainable coating technologies for pretreatment of aluminium surfaces.
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4.4 MacDermid GmbH, D-Forst
The MacDermid company offers various alternative pretreatment processes. These have been used
for many years in numerous factories in Germany and other European countries.
The performance of the systems offered by MacDermid has been documented in numerous studies
and also by certifications from various quality communities (including GSB International). An overview
of the various systems and their certifications and properties is shown in the following table.
Of crucial importance for the performance of MacDermid's alternative systems is compliance with
prescribed rinse criteria in the rinsing before - and in the event that downstream rinsing is required -
after the actual conversion bath. Contamination with foreign materials must be avoided. Similarly, a
corresponding bath analysis and process monitoring is recommended. The specific and balanced
combination of MacDermid process chemicals leads to a significant reduction in the process costs of
the pretreatment (in direct comparison to conventional chromating processes). All MacDermid
processes are suitable for dipping and spraying applications. In particular, Iridite CF is also suitable for
a multimetal pretreatment prior to powder coating.
Overview of MacDermid pretreatment processes:
Product name: Basis No-rinse
process Certifications Number of
reference systems Specifics
Iridite EXD Zr No GSB International (stage 3
pending)
Qualicoat
Customer-specific
10 Purely inorganic composition
Special drying behaviour
Particularly suited to polyamide thermal seals
Iridite CF Ti/Zr Yes GSB International
Qualicoat
Customer-specific
15 Multimetal capability
No after-rinsing required
High bath stability
Iridite NCP Ti/Zr No Qualicoat
Customer-specific 3 Blank corrosion protection
Iridite NR2-I Ti/Zr Yes Qualicoat
Customer-specific 10 Coil Coating
Iridite NR4-T Ti/Zr Yes With integrated UV tracer
In the test phase
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4.5 Nabu-Oberflächentechnik GmbH, D-Stulln-Nabburg
4.5.1 Chromium-free pretreatment with Nabutan 310
As is so often the case, Germany seems to ahead of the game when it comes to introducing
environmentally sound processes. For more than 10 years, therefore, chromium-free pretreatment
processes have been established on the market, meaning that various practical processes are now
available. Chromium-free pretreatment due to the ROHS Directive, the EU ELV Directive or regional
regulations, has today become a real alternative to yellow or green chromating.
What exactly is meant by "chromium-free pretreatment with Nabutan 310"?
Chromium-free pretreatment means: The passivation of the aluminium surface without chromium (VI)
or chromium (III) compounds in the bath and in the deposited conversion coating that is applied to
promote adhesion and inhibit corrosion. Of course, in these processes, the degreasing and pickling
process is also chromium-free. Before the powder coating, the aluminium profiles are not protected by
standard yellow or green chromating, but are subjected to a titanium- and polymer-containing
pretreatment, which is 100% free of toxic, carcinogenic chromates.
With a classic yellow chromating, the application parameters are clearly known and defined. The
operator estimates the low-maintenance bath control and the uncomplicated application. On the other
hand, the environmental incompatibility or the dangers of chromium (VI) to humans must not be
underestimated. The recurring debate on this serious issue should continue to incite us to reflection in
the future. If it were merely a matter of technical merits, then yellow or green chromating would be
hard to beat. They always pose a challenge to chromium-free alternative systems.
30
With the awarding of the contract, the contractor or architect, as the user of coated aluminium profiles
and sheet materials, can decide whether to select a traditional "yellow chromating" as the corrosion
protection or an environmentally friendly chromium-free pretreatment with Nabutan 310, which is
almost equal in all respects to chromate pretreatment.
4.5.2 Certification testing for Nabutan 310
No new product group in recent years has been more carefully tested than chromium-free conversion
layer formers. In addition to leading quality organisations, façade builders, pressing plants, automobile
manufacturers and research institutes have been working with chromium-free conversion layers from
individual providers. In the example of Nabutan 310, the previous quality assessments are collected.
When properly applied, they give the operator the confidence to meet the high demands of the market.
4.5.3 Approval in the process regulation 92049 BMW Group
BMW approved the titanium-based pretreatment process with Nabutan 310 for the pretreatment of
aluminium casting alloys and aluminium wrought alloys in 2004.
4.5.4 Qualicoat Product Approval
Nabutan 310 was tested in 2003 by Qualicoat and received approval as an alternative pretreatment.
The repeat tests have so far all been completed positively.
4.5.5 GSB International quality community
In 1998, the product Nabutan 310 received the provisional certification from GSB International
according to GSB International Stage 3 of the material certification process for the powder coatings
sector. Under certification number 302 a, after a three-year exposure without any problems, the final
certification was issued in 2002. The recurring annual tests from the current production lines have all
been passed to date.
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4.5.6 Results from 10 years of exposure at Hoek van Holland
In 1998, GSB International exposed chromium-free pretreated and coated plates at Hoek van Holland,
a suburb of Rotterdam. The prevailing maritime industrial climate there is ideally suited for exposing
the powder paint-coated aluminium samples to weathering tests.
The Nabutan 310-pretreated plate and profile sections, even after 10 years of exposure, still showed
no significant signs of corrosion or adhesion problems. In Hoek van Holland, where the samples were
exposed to intense sun and aggressive sea air, the reliability of the Nabutan 310 system was
confirmed.
Image: Weathering in Hoek van Holland, NL
The plate and profile sections originated from a plant test of GSB International Stage 3, performed
under production conditions at a GSB International coating company. The test results in the short-term
studies, such as ESS and FFK, essentially confirm the results of the exposure at Hoek van Holland
over a period of 10 years. This shows that environmentally friendly processes do not need to be a step
backwards, and there is now enough experience to apply the alternative processes correctly.
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4.5.7 Summary
The use of chromium-free alternatives does not necessarily mean sacrificing quality. With proper use
of the product, the corrosion protection is similar to that of a conventional chromating. In contrast to
chromating, Nabutan 310 poses no problems for the environment, and is thus easier in terms of the
storage and handling of chemicals. However, the superior environmental performance is accompanied
by a higher sensitivity of the process, which often means that alternative pretreatments are unjustly
labelled as being complicated.
In fact, with a chromium-free process, users get a somewhat lower flexibility and sometimes even
more sensitivity in the pretreatment process. Thus, the operation mode of galvanised steel and
aluminium in the same pretreatment chemistry is critical. But even with the use of yellow or green
chromating, a mixed operation mode can lead to unwanted electrochemical depositions on the
aluminium material and negatively affect the corrosion protection. Care is therefore recommended for
any type of chemical pretreatment.
If the chromium-free pretreatment process is well monitored, the bath chemistry including rinsing is
analysed, and the chemical additions are automated as far as possible with control units, this
sensitivity can be counteracted. It is precisely these measures that lead to a more intensive process
control, which ultimately contributes to an increase in quality.
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4.6 SurTec International GmbH, D-Bensheim
SurTec 650 is certified by GSB International as an alternative pretreatment system with chromate-free
layers under certification number 308 a. It has been used since 2005 in the non-construction sector
and since 2008 in the construction sector in Germany. SurTec 650 meets the requirements for
corrosion testing in the Sea Proof Plus weathering class (FFK: F = 0, 1000 h) and is therefore ideally
suited for mass production at the highest level of quality.
In addition to the relevant standards for the construction industry, the requirements of the aerospace
industry (e.g. blank corrosion in the salt spray test > 168 h), the electronics industry (e.g. surface
resistance) and the automotive are met; for this reason, SurTec 650 is also optimally suited for coaters
with a large variety of products. The product SurTec 650 is exempt from labelling requirements.
Precise bath control is possible via a simple analysis of the active substance by means of photometry.
SurTec 650 is a never-dump process; therefore, no new preparation of a bath solution is necessary.
By replacing chromium (VI) technology with SurTec 650, process cost savings of up to 30% can be
realised.
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5 The current development status of chromium-free processes from the perspective of the
coaters
5.1 General information
The following contributions reflect the opinions and experiences of the companies. The
content is solely the responsibility of the coaters.
GSB International currently has 80 coaters as members, 33 companies of which use chromate-free
and chromium-free surface pretreatments. The following examples describe some past experience in
the use of chromium-free pretreatment processes.
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5.2 Alulux Beckhoff GmbH & Co., D-Verl
Alulux is one of the world's leading manufacturers of roller shutters and garage door systems made of
aluminium. The prefabricated shutter and garage door brands are optimally tailored to the needs of
specialist customers. Longevity, the use of high-quality materials and the development of individual
solutions are natural requirements. Production to precise dimensions and also the comfort automation
of the roller shutters and garage door systems are performed entirely according to requirements.
Since 2002, in the prestage to the powder coating, Alulux has been using a chromium-free surface
pretreatment from the company NABU.
The process steps are degreasing, rinsing, pickling, fully desalinated water rinsing, and chromium-free
conversion coating.
The experiences with chromium-free preanodising have been entirely positive and have met with
strong recognition from the Alulux clientele.
Some building images:
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5.3 Alumil-Milonas Aluminium Industry S.A., GR-Kilkis
In early 2008, the company Alumil began to use the chromium-free pretreatment as a conversion layer
for powder coating in its horizontal and vertical coating plant for aluminium profiles.
From the beginning until now, products from different suppliers were used both in the horizontal and
vertical plants, which are constantly being tested and evaluated during production. All these products
have a certification from GSB International and Qualicoat.
Pretreated and coated amounts:
In parallel to the production process, laboratory tests and evaluations are conducted to obtain data for
the optimal operating conditions; emerging problems can also be analysed here.
Horizontal system
Year Experiment time Chemical
manufacturer Product Pretreated quantities (kg)
2008 2 months A 1 750.000
2008 3 months B 1 1.150.000
2008 3.5 months C 1 860.000
2009 5 months C 1 1.200.000
2009 3 months B 1 580.000
2009 4 months A 2 950.000
2010 12 months A 2 2.250.000
2011 2 months D 2 100.000
2011 7 months A 2 670.000
Vertical system
Year Experiment time Chemical
manufacturer Product Pretreated quantities (kg)
2008 4 months E 1 4.500.000
2008 8 months A 2 5.750.000
2009 12 months A 2 7.000.000
2010 10 months A 2 5.600.000
2010 2 months E 2 1.400.000
2011 2 months A 2 950.000
2011 6.5 months E 2 5.000.000
2011 0.5 months D 2 380.000
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Our previous experience with the use of a chromium-free pretreatment are:
1. It is important that the supplier knows his product perfectly.
2. A crucial factor is the adjustment of the product application to the particular characteristics of
the production line.
3. The properties of the coating, apart from the chemical process, seem to have significant
influences on the painted end product.
4. The user must have both a well-equipped laboratory with all necessary equipment and also
well-trained personnel.
5. The user must ensure a continuous and systematic bath monitoring of the product parameters
(concentration, conductivity, pH, temperature, coating weight, etc.).
6. Each coating line should be equipped with the necessary equipment (dosing pumps,
conductivity, pH, cooling and heating, etc.) to ensure the stability of the product.
7. The use of newly certified products alone does not ensure smooth execution.
Some of our objects that have undergone chromium-free pretreatment since 2008:
Image: Blue Ridge - India Image: Seaside Hotel in Sirte - Libya
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Image: Khan Shatyr Project - Kazakhstan
Image: American University - Iraq
39
Image: Jasmin Tower - Katar Image: Reem Tower in Abu Dhabi - UAE
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5.4 heroal – Aluminiumgesellschaft Hövelhof mbH & Co. KG, D-Verl
The company heroal is a GSB International premium coater and operates three coating lines, of which
two plants work with yellow chromating and one plant works with a chromium-free surface
pretreatment. Chromium-free passivation has been in use for about 2 years in the painting plants,
aluminium is coated exclusively. Since the introduction of the chromium-free surface pretreatment in
the plant, well over 500,000 m2 of chromium-free pretreated aluminium profiles have been coated. The
dosing technology in all areas of the pretreatment is an important point for product safety. Another
important point is to control and document the bath parameters.
It is already clear that, in the future, even more objects will be tendered for chromium-free
pretreatment, so the company heroal is well prepared if the legislator prohibits the use of chromium
(VI).
Another advantage of the introduction of chromium-free pretreatment is that there are no longer any
expenses for chromium-containing waste water; we also protect our employees and contribute to the
environment.
Already, a new coating plant with chromium-free passivation is being planned, resulting in reduced
regulatory requirements for obtaining the operating licence.
41
5.5 LOV-Limbacher Oberflächenveredelung GmbH, D-Limbach-Oberfrohna
More than 12 years of practical experience with chromium-free passivation in spraying processes at
LOV.
Authors: Dipl.-Ing. Michael Kirmse (GF), Dipl.-Ing. Jörg Seiche (QMB)
5.5.1 Introduction
Limbacher Oberflächenveredelung GmbH is today a medium-sized enterprise in the field of powder
coating and industrial wet painting with 40 employees. Since its foundation in 1998, the company has
grown from a workshop into a high-quality industrial enterprise. The most important milestones in this
context were the attainment of product qualification for outdoor aluminium according to DB TL 918340
(certification for rail vehicles) in 2003, the certification according to ISO/TS 16949 in 2004 and joining
GSB International in 2009 as a master coater. In addition, LOV GmbH is a founding member of the
IQC. These certificates and approvals constitute evidence of quality by external monitoring, which
provides each customer with reassurance regarding the coating of its products.
This includes the continuous improvement of processes and workflows. This led in 2008 to a new
investment at the Limbacher Oberflächenveredlung site. As part of this new building, one of the most
advanced coating plants in Europe was constructed. In doing so, the very latest technology was
implemented. Highlights worthy of mention include: a highly flexible power-and-free conveyor system,
a trication zinc phosphating for the pretreatment of steel or galvanised steel, a chromium-free
passivation for aluminium (retaining the same technology as the previous plant) with the highest
possible corrosion requirements and coating in two ultramodern powder coating booths.
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Image: 2-part pretreatment plant LOV Image: Pretreatment testing LOV
Image: Powder coating line of LOV with two powder booths
5.5.2 Chromium-free passivation
As already mentioned, LOV GmbH can look back on over 12 years' experience with chromium-free
passivation and was a pioneer in the Europe-wide trend towards conversion to Cr (VI)-free
pretreatment systems. As early as 1999, it already ensured that the system to be used met the
guidelines of GSB International. This product based on titanium and polymer is completely chromium-
free passivation, which also satisfies the ROHS Directive and the EU Directive on ELVs, and has been
used in LOV from the start as a no-rinse system.
43
In contrast to classical chromating systems, chromium-free systems, however, place much greater
demands on monitoring (titration, shift weight determination, conductivity) and bath maintenance of the
active and also the rinsing baths. Of particular note here is that the coating weight determination, due
to the small layer thickness in the nanometre range, is not performed by weighing-out, as in classical
systems, but is done photometrically. This method is also more accurate, meaning that there is less
room for error. Since the chromium-free passivation itself produces virtually no pickling attack on
aluminium, the optimal effect of the pickling degreasing must also be observed here.
In addition, these systems react very sensitively to carryovers, especially with foreign ions, which then
generally lead to immediate rejection of the passivation chemistry. Therefore, these systems are only
very limitedly or not at all suitable for a mixed mode of operation with metals other than aluminium.
Equally important is the production of an optimal rinsing criterion prior to passivation.
44
It is important in this regard to make sure that rinse 1 is not too clean, i.e. conductance in this rinse is
too low. Furthermore, the conductance in the fully desalinated water circulation rinse with maximum 10
µS may not be exceeded, since this would otherwise result in an excessive load on the surface with
foreign ions and hence a deterioration in the corrosion resistance.
These conditions have been established at LOV since 1999 and we have thereby gained the
experience that, when the right conditions are present, results are achieved which are absolutely
equal to those achieved with classical systems.
In the new investment in 2008, we incorporated these experiences into the planning of the
pretreatment plant. This was done in detail by the following measures:
Creation of a separate pretreatment line for aluminium only
Creation of defined overflows into the active baths pickling degreasing and passivation
Automatic addition of the preparation chemicals to the active baths
Consistent setting of a defined cascade between the rinsing 1 and rinsing 2
Fully desalinated water rinsing not as a basin rinse, but by direct loading of the parts via their
own spray register with direct outflow to water treatment via an ion exchange system
These additional measures subsequently turned out to be extremely positive. Because of the constant
overflow of the pickling degreasing, complete rejections are no longer necessary. Only partial
rejections occur in the regular cleaning work as part of predictive maintenance. In addition, the
passivation has an almost infinite lifetime due to these measures. Only for cleaning the bath walls is
draining off of the passivation into the opposite container necessary, whereby the chemical is 100%
pumped back in after cleaning.
With regard to corrosion resistance, our chromium-free passivation based on titanium/polymer met our
customers' requirements in nearly 100% of application cases. In addition, with its passivation system,
LOV GmbH has met the criteria of the Sea Proof Plus seal of GSB International without further ado,
which underlines the impressive performance of this system.
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5.5.3 Examples of implemented projects:
Image: Representative office building in the centre of D-Chemnitz/Saxony
Image: Library Of Birmingham (Facade manufacturer: Lindner Fassaden GmbH, D-Arnstorf)
46
5.6 TK-Oberfläche GmbH, D-Bielefeld and PBS Schreiner GmbH & Co. KG, D-Grebenau
We have more than 12 years of practical experience with a chromium-free surface treatment in dipping
and spraying processes, which are certified by GSB International.
5.6.1 Introduction
Because of the changes in the 1980s with regard to the environment and corrosion requirements for
powder-coated parts used outdoors, intensive research efforts were undertaken especially in the field
of pretreatment.
It was foreseeable that existing systems, such as chromating and phosphating, were no longer able to
meet all of the requirements of the industry. The results of the nearly 10 years of developments in the
field of chromium-free pretreatments could then be transferred to a pilot phase or customer trials at the
end of the last millennium.
5.6.2 Process description
Process sequence for alkaline dipping:
Process sequence for alkaline spraying:
TK-Oberfläche company PBS Schreiner company
Alkaline etching degreasing Alkaline etching degreasing
Coil 1 Coil 1
Coil 2 Coil 2
Fully desalinated water coil Coil 3
Desmutting Desmutting
Coil 1 Coil 1
Coil 2 Fully desalinated water coil 1
Fully desalinated water coil Fully desalinated water coil 2
Fully desalinated water coil 3
Chromium-free conversion Based on titanium
Chromium-free conversion Based on titanium
Process sequence for dipping (left) and spraying pretreatment (right)
47
As with almost all surface-finishing processes, pretreatment consists of the steps of degreasing,
etching/desmutting/activation (adhesion creation and corrosion protection), which are interrupted by
rinsing steps. In the case of chromium-free pretreatment - in comparison to other passivations - extra
attention must be paid to the rinse steps, since the success of the process is extremely vulnerable to
contaminants. Ultimately, by observing all of the process parameters, we can obtain a homogeneous
titanium fluoride polymer layer on an aluminium component, which serves as the optimal substrate
with extremely good corrosion protection properties for a subsequent layer of powder.
The almost unlimited service life of the chromium-free process (only partial rejections are necessary if
properly maintained) not only reduces disposal costs and environmental risks but also considerably
reduces the cleaning required and the health risks to employees.
Image: Scanning electron micrograph images (left) and top view of chromium-free layer (right)
To the chromium-free pretreated profiles, in a powder booth, a 50-120 μm thick layer of powder
(selected according to requirements) is applied by spray guns (corona or tribological loading) and
cross-linked (fused) by annealing at approx. 200 °C. In this way, aluminium components can be given
corrosion protection that meets the GSB International requirements for resistance to filiform corrosion
(DIN EN 3665) as well as the tests in the acetic acid salt spray test (DIN EN ISO 9227).
Image: Example of a powder booth The following image shows the schematic structure of a powder-coated component. Here, the small
layer thickness of the effective chromium-free coating is remarkable.
48
Image: Schematic representation of a powder coating on aluminium
Image: Photometric measurement principle for layer weight determination 5.6.3 Testing criteria
The introduction of a chromium-free pretreatment must - due to its specific needs - lead to a changed
working method for a coating company.
For example, test panels must be operated regularly with production batches in which, by cross-
cutting and boiling test, Erichsen cupping, mandrel bending test and cutting test, and a 1000 h ESS
test (DIN EN ISO 9227), both adhesion and corrosion protection are checked. Appropriate tests and
their results are shown in the image below. In addition, the correct setting of the bath chemistry must
be determined regularly. This is ideally done by a determination of the deposited layer thickness. As
an auxiliary measure, we here determine the layer weight. In the next image, the sequence of the
photometric determination is shown schematically. Alternatively, a determination by XRF can also be
performed (X-ray fluorescence analysis) with which we only determine the amount of deposited
titanium.
49
Image: Test panels after adhesion test (left) and profile section after 1000 h ESS (right)
5.6.4 Summary and outlook
Looking back on more than 12 years of successful work with a chromium-free no-rinse pretreatment in
mass production, it can be said that not only is it equal to the current chromating and phosphating in
respect of its process safety and properties, but even constitutes enhanced protection, also supported
by improved environmental and employee protection and lower disposal costs.
Through the combination of a chromium-free pretreatment with highly weather-resistant or PFTE-
containing powder coatings, we at TK-Oberfläche GmbH and Schreiner GmbH & Co. KG can offer our
customers the best and also the most environmentally friendly powder coating in the market. In this
context, all of the relevant EU directives on the EU ELV directive and the ROHS or WEEE (popularly
known as the "e-waste regulation") are fulfilled, even for the construction industry. With this
combination, there are now only a few other companies in Europe in the industry who can offer their
customers these two advantages together.
Therefore, in all respects, it is a successful process introduction. The following images of the buildings
equipped with our coating stand as living witnesses to the very positive experiences since the process
conversion, with which our courage was rewarded.
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Property images:
Image: University Clinic of Mainz (PBS Schreiner, D-Grebenau)
Image: University Clinic of Frankfurt-am-Main (PBS Schreiner, D-Grebenau)
51
Image: DonStroy, Moscow (TK-Oberfläche, D-Bielefeld)
Image: Mövenpick Hotel, NL-Amsterdam City Center (TK-Oberfläche, D-Bielefeld)
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5.7 Warema Renkhoff SE, D-Marktheidenfeld
Warema Renkhoff SE operates 2 powder coating lines, each equipped with a 6-chamber cycle plant
for pretreatment.
The pretreatment involves the following process steps: Alkaline pickling degreasing, acid pickling,
passivation, and the necessary rinsing steps. Until the end of 2008, a yellow chromating was used for
passivation.
Due to the increasing demand for chromium-free pretreated surfaces, the many years of positive
testimonials for chromium-free surfaces, the prohibition of chromium (VI) compounds in the automotive
industry and electrical engineering and the associated uncertainty in the market regarding chromium
(VI) certifications, Warema Renkhoff decided to convert to chromium-free pretreatment in the new year
2008/2009.
Since the two pretreatment plants possessed a common fresh water supply, rinsing water preparation
and waste water processing, it made sense to make the switch in the pretreatment on both plants
simultaneously.
The plant cleaning, which must be done very laboriously and thoroughly in the conversion, was
performed together with the company Buchen Umweltservice GmbH. In the first step, the adherent
chromate compounds were partially dissolved with sodium hydroxide and hydrogen peroxide and then
the remaining encrustations on the plant were removed by means of high-pressure cleaning and
rinsing. The resulting highly concentrated waste water from the cleaning was disposed of externally,
and all other effluent was treated in the company's own waste water system.
To ensure the absolute purity of the surfaces before the chromium-free pretreatment, the rinsing water
ducts in the pretreatment plant were rebuilt. Since the chromium-free pretreatment is used as a no-
rinse process, a chamber for an additional rinsing process was available. Thus, it is possible to
operate the pretreatment with 2 rinsing chambers (containing multiple rinsing steps) between acid
pickling and chromium-free passivation. The carryover of foreign ions into the chromium-free
passivation bath is almost impossible, thus forming the basis for good and reliable corrosion
protection.
The control of the passivation layer can be performed with simple tools in the company laboratory. On
site, additional control and monitoring measurements were installed to stop the pretreatment
immediately if the chromium-free passivation process is disrupted.
53
This ensures that all parts are given the necessary corrosion protection, which is not optically visible,
in contrast to yellow chromating.
A decisive advantage after the switch to chromium-free pretreatment was improved corrosion
protection of the surfaces against filiform corrosion.
Furthermore, the waste water system became more flexible, since all waste water could be processed
either in one or the other waste water plant.
Due to the increased purity requirements in the pretreatment, more fresh water was consumed and
thus more waste water accumulated, but the specific consumption of waste water chemicals and
specific sludge accumulation were lower than with the use of chromating. The fully desalinated water
plants for the preparation of the rinse water can be operated for longer until a regeneration is required,
because the rinse water is less contaminated. And, of course, it must not be forgotten that the staff is
spared from handling hazardous chromium compounds.
Meantime, Warema Renkhoff SE has an impressive number of objects that are equipped with sun
protection products with chromium-free pretreated surfaces.
Some object examples:
54
55
6 Chromium-free pretreatment for coil coating
6.1 Hydro Aluminium Rolled Products GmbH, D-Grevenbroich and Novelis Deutschland
GmbH, D-Göttingen
The following contributions reflect the opinions and experiences of the companies. The content is
solely the responsibility of the company.
6.1.1 General information
In the coil coating process, rolled coils of aluminium are continuously coated with paint or foil. After
coating, they are re-rolled into coils, and then cut with a processor according to their use as a roof or
wall panel, window profile, blinds, signs, etc., cut, die-cut, profiled, deep-drawn, jointed or glued
together.
Aluminium surfaces must be protected against corrosion prior to painting by a suitable chemical
pretreatment. For decades, chromate-containing chemicals were used for this surface treatment.
Since these are classified as hazardous to health, carcinogenic and harmful to the environment,
chromate-free and chromium-free systems have been in development in the coil coating industry since
the 1980s. Chromium-free pretreatments and chromate-free primers have been available on the
market since the mid-1990s.
Coil-coated aluminium is used in general industry, but in larger quantities also in the packaging
industry. Here, chromium-free processes were in use in some fields as early as the 1970s. The
following discussion refers to the industrial application, however. The use of coil-coated aluminium as
packaging is not discussed here.
In the field of general industry, the construction industry is the largest market for coil coating,
accounting for around 70%. Therefore, this discussion will be restricted to that segment.
Regarding a survey of construction companies and coil coating processors, as reported by GE Betz in
November 2002 at the Congress of the European Coil Coating Association (ECCA) in Brussels (David
Ellis, GE Betz, "Chrome Use In Building Products: An Industry Perspective") it was already apparent in
2002 that two thirds of all respondents after the first evaluation of the results with chromium-free
coatings assumed that the quality of chromium-free coated plates was comparable to that of
chromate-containing plates, and chromium-free coatings would become widespread in the future. At
that time, chromium-free pretreatments had been on the market for about 6 years.
56
Since 1994, chromium-free primers on steel or galvanised steel have been used in the coil coating
industry. In 1997/98, this was followed by the introduction of chromium-free pretreatments in the steel
industry.
In the aluminium industry, due to the specific properties of aluminium, chromium-free systems have
already been known for even longer.
The details presented here regarding chromium-free coatings in the coil coating industry are mainly
based on the results of a project developed by the ECCA Group in Germany, under the leadership of
Marcus Schinzel, of Chemetall, in late 2005.
6.1.2 The coil coating process
6.1.2.1 Overview
Aluminium products made from coil-coated coils and sheets are characterised by consistent quality,
exceptional formability, corrosion resistance and abrasion resistance, and a variety of colours, gloss
levels and surface textures. The production process typically involves the following steps:
Cleaning
Conversion treatment (pretreatment)
Possibly the application of a primer
Top coating or film coating
6.1.2.2 Cleaning and degreasing
The coil coating process requires a clean, well-prepared surface of the metal coil, if a long-life product
is to be created that has an aesthetic appearance and high durability in all environmental conditions.
Cleaning and pretreatment of the coil are performed in separate zones of the coil-coating system
immediately before coating.
The cleaning of aluminium coils includes both alkaline and acidic cleaning steps. The cleaners remove
corrosion products and release agent residues from the surface and ensure that the surface is
wettable. Two rinsing steps followed by an acid pickling, often based on sulphuric acid and fluorides.
In this step, the oxide layer and accumulations are removed from the alloy components. The strength
of pickling attack is controlled by the fluoride concentration. In the final step of cleaning, the excess
cleaner is removed by means of nip rolls and thoroughly rinsed with water in several stages.
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6.1.2.3 Chromium-free surface pretreatment
As soon as the cleaning process has created a clean, water-wettable surface, the now highly reactive
metallic surface must now be covered with an anti-corrosion layer, which also provides an adhesive
substrate for the subsequent paint layer. This is achieved by chemical processes for the conversion
treatment of the metal surfaces.
Chromium-free pretreatment chemicals nowadays offer adequate corrosion protection and adhesion
for subsequent coatings. Strong correlations and the comparability of chromium-free and chromate-
containing pretreatments in various natural weathering and accelerated corrosion tests have been
reported.
In general, the chromium-free chemicals are based on aqueous solutions of transition metal
complexes and compounds, for example, titanium and zirconium compounds, as well as on specific
water-soluble polymers. They generate defined layers that can be characterised analytically, e.g. by
means of Auger electron and photoelectron spectroscopy.
The mechanisms of adhesion and corrosion resistance are attributed to a metal oxide layer that forms
in a first reaction phase on the treated sheet and is then covered with the organic matrix.
Pretreatment solutions are applied by spraying, dipping, or dipping/squeezing. More frequently,
however, the no-rinse process is used today. Here, a liquid film only a few micrometres thick is applied
to the coil with a roller. This film is dried, thus forming a corrosion-protective, adhesion-promoting solid
layer. In the application by means of a roller coater, there are no excess chemicals or products of
secondary reactions on the surface, which eliminates any need for subsequent rinsing. This in turn
eliminates the need for huge amounts of rinse water and its disposal issues.
Pretreatment procedure Chemical basis Application Overflow
approx. 10-100 l/h
Rinse chromating Cr(VI) / H3PO4 / HF Spraying/dipping + squeezing + rinse Yes
No-Rinse chromating Cr(VI) / Cr(III) / (SiO2) Chemcoater or spraying/dipping +
squeezing No
Rinse chromium-free H2TiF6 / H2ZrF6 Spraying/dipping + squeezing + rinse Yes, but no chromium (VI)
No-rinse chromium-free H2TiF6 / H2ZrF6 / organic
chemistry
Chemcoater or spraying/dipping + squeezing
No
58
Pretreatment procedure Carryover
approx. 5 mL/m³
Handling Work hygiene
Rinse chromating Yes - Chromate
No-Rinse chromating No (+) Chromate, no waste water
Rinse chromium-free Yes, but no chromium (VI) + Chromate-free + waste water
No-rinse chromium-free No + Chromate-free + waste water
Table: Pretreatment processes - application / waste water technology / handling
(Source: ECCA-Gruppe Deutschland e. V., Germany)
The chromium-free pretreatments are based on aqueous, non-toxic transition metal complexes and
special water-soluble polymers. For the reaction, the following model was developed [Deutsche
Forschungsgesellschaft für Oberflächenbehandlung e. V., Deutsche Gesellschaft für Galvano- und
Oberflächentechnik e. V. (Veranst.): Light metal applications (Düsseldorf 2004). Düsseldorf: DFO,
2004–Report Vol. No. 57 – Wendel, T.: Vorbehandlung von Aluminium-oberflächenwerkstoffen vor
dem Fügen im Automobilbau [Pretreatment of aluminium surface materials prior to bonding in the
automotive industry] and
Schubach, P.: Chromatfreie Vorbehandlungsverfahren für Aluminiumwerkstoffe [Chromate-free
pretreatment processes for aluminium materials]. In: Galvanotechnik 92 (2001), Issue 7, pp. 1825-
1834]:
In the first reaction step, the acidic chemicals attack the surface, thus generating a metal oxide layer at
the interface. At this interface, phosphorus and crystalline lattice cations, for example metal ions, are
included, which are present in the substrate and in the pretreatment chemical The metal oxide layer
ensures adhesion and corrosion protection. It is then covered by an organic layer. The polymers
cause the fixation of the inorganic components by complexation and, secondly, form a barrier layer.
The following table shows the results of various tests, in which aluminium sheets (AA 3005) were
pretreated after an either chromate-containing or chromium-free acidic cleaning. Both panels were
then provided with two chromium-free polyester paint systems. The results show that the chromium-
free pretreated sheets have the same properties as the chromate-containing pretreated sheets. Both
systems meet the requirements with regard to corrosion protection.
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Table: Comparison of the corrosion protection of chromium-free and chromate-containing
pretreated samples
(Source: Chemetall GmbH, Germany)
6.1.2.4 Chromium-free primers
The pretreatment prepares the metal surface for painting. As the first organic layer, a base coat is
applied, known as the primer. It serves as a bonding agent between the pretreated metal and the
colouring topcoat and controls the corrosion protection of the entire paint application.
At the end of the 1980s, chromium-free corrosion-inhibiting pigments were increasingly introduced
onto the market from the raw materials industry. It thus became possible to formulate chromium-free
primers for the coil coating industry too.
Today, modern coil coating lines make use of primers suitable for many applications due to their high
quality standards. Such universal primers are based on specific binding agents that are combined with
active corrosion-inhibiting pigments to enhance the adhesion and corrosion properties. They are
optimised to effectively adhere to any substrates, on steel as well as on aluminium. They can be
painted over with all solvent-borne topcoat types in the coil coating process.
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6.1.3 Topcoats
The field of architecture requires special deformation properties and surface hardness, and the
outdoor area calls for corrosion and weathering resistance. For these applications, polyester,
polyurethane or HDP topcoats, PVC plastisols and PVDP topcoats can be used in an almost unlimited
range of colours.
Some colour shades, in particular older ones, are still made with lead chromates or lead-molybdenum
chromates, because in some cases the customer can accept no deviation from the original proposals.
This is especially true for colours in the yellow, red, green and brown shades.
According to REACH, lead pigments may no longer be used after 30.11.2013. For some time now,
however, there have been lead chromate-free substitute pigments with an inorganic or organic basis
(Eckhart Korona, BASF SE, "Lead-Free Pigments For Coil Coating" ECCA Congress, Brussels,
22./23.11.2010). They sometimes have a very similar colour to the original lead chromates or lead-
molybdenum chromates, but are slightly more expensive than the currently used pigments. There is
currently also difficulty in replacing the bright orange shades. Research efforts are being made in this
regard to find solutions.
6.1.4 Field reports
6.1.4.1 Aluminium roller blind coil
For aluminium roller blind coils, in the ECCA Project 2005, a comparison was made between the
standard chromium (VI)-coated and chromium-free coated coils. As can be seen in the table, there are
no differences in properties between the two samples.
Product: Roller blind coils
made from coil-painted aluminium
Alloys: AlMg0,5Mn1; AlMg1Mn0,5
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Testing Testing
standard Standard Cr(VI) No-Rinse Cr-free pretreatment
Bonding agent base PUR/PA
(polyurethane/polyamide) PUR/PA
(polyurethane/polyamide)
Adhesion and crack
resistance at the narrow
collar (hook and drip rail)
PA 0050
T0 break-free, crack-free T0 break-free, crack-free
Heat resistance at the T-
bend DIN EN
13523-13 Unchanged Unchanged
Erichsen cupping DIN EN
13523-6 No peeling paint until metal
cracking under Tesa test No peeling paint until metal
cracking under Tesa test
Condensation water -
constant climate
(Humidity test)
DIN EN ISO
6270-2
1000 h No changes No changes
Water dipping resistance
(Waterlogging)
DIN EN
13523-9 No changes No changes
Acetic acid salt spray test
(Corrosion test)
DIN EN
135239227
1000 h
Grade 1 to 2 on undeformed
surface, incipient crack on
narrow collar and cutting edge
Grade 1 to 2 on undeformed
surface, incipient crack on
narrow collar and cutting edge
Grade 1: very good; grade 2 good; grade 3: satisfactory; grade 4: sufficient; grade 5: deficient
Table: Properties of chromate-containing and chromate-free pretreated samples
(Source: ECCA-Gruppe Deutschland e. V., Germany)
6.1.4.2 Laboratory building – Henkel KGaA, D-Düsseldorf
In 1998, during the renovation of two laboratory buildings was conducted by Henkel, a reference
building for the chromium-free coil pretreatment was created. In co-operation with the company Hydro
Aluminium Rolled Products GmbH in Grevenbroich, the aluminium façade coil and primary material for
sun protection plates were equipped with a pretreatment developed by Henkel (Alodine® NR 1453)
and coated with a monolayer high-performance polyester paint.
From the sheet material, trapezoidal panels and sun protection covers (so-called interior blinds) were
created, with which, in October 1998, the staircases and window rows on the south façade of both
62
buildings were covered. The entire surface area measured approximately 400 m² of trapezoidal panels
and 800 m² of sun protection roller blinds.
The façades have been exposed for more than 10 years to sunlight, wind and weathering in an
industrial environment, and in the loading areas also to mechanical damage. The silver metallic paint,
however, shows no signs of corrosion damage, even at critical points such as punching holes, bolt and
screw connections or drip rails. The high performance level of chromium-free pretreated, coil-coated
aluminium plates for building applications has thus been demonstrated most impressively.
The chromium-free
pretreated trapezoidal
panels show unbroken
drip rails, even after 10
years of weathering.
Sun protection venetian
blinds made from coil-
coated panels
6.1.4.3 Chromium-free pretreated roof and wall cladding
For over 10 years, Novelis has been supplying chromium-free pretreated aluminium for roof and
façade elements from its factory in Bresso, Italy. In the Göttingen plant, the pretreatment is applied in
the no-rinse process. Since 2005, a few product groups with chromium-free pretreatment have been
manufactured here, and the percentage of such products has gradually expanded. Both plants use
alloys of the 1000, 3000 and 5000 series. The roof and façade elements usually have a 2-layer
construction with a chromium-free pretreatment and a chromate-free primer.
63
The two images show an office building with a coil-coated façade, built in 2002 in Darmstadt, and a
residential building with roof panels made from painted aluminium, built several years ago in Austria.
Both buildings continue to have a flawless appearance today. Both materials have undergone
extensive testing, in accordance with their future use, and specifically manufactured with chromium-
free pretreatment. Compared to the old pretreatment containing chromium, no deterioration could be
detected in these applications, even after several years.
Image: For the façade of this office
building in Darmstadt (Germany), which
was built in 2002, chromium-free
precoated aluminium elements were used
Image: The roof of this residence is made from
chromium-free pretreated roof elements
6.1.5 Summary
Chromium-free pretreated and, if necessary, primed coil-coated aluminium has been on the market for
more than 10 years and is accepted by customers. The weathering results show that the use of
chromium-free pretreatments in no way leads to inferior results. In some cases, they were even
marginally better, because during the conversion optimised primer or base coats could be used.
The conversion of the topcoat to chromate-free systems will occur after the REACH-prescribed cut-off
date for the use of lead chromates at the end 2013. Replacements are already partially available on
the market. For some critical colours, like bright orange or red shades, solutions are currently being
developed.
64
A model for the adaptation to the environmental and technical conditions is Deutsche Post: As early as
the 1980s, it deliberately changed the yellow colour to permit the use of lead chromate-free
pigmentation. An important external sign of its corporate identity was thus made more environmentally
friendly and material-conscious.
In addition to the construction industry, there are also markets, for example in aircraft construction,
where there are currently no alternatives to the use of chromate-containing coil coating. Here, partially
for safety reasons, chromate-containing systems continue to be used.
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7 Preanodisation
Another environmentally friendly alternative passivation of the aluminium surface is the generation of
thin aluminium oxide layers, referred to as preanodisation.
Preanodisation has been successfully used in the construction industry for several years. It is applied
especially with locations of buildings near the coast, in aggressive industrial climates or application
areas particularly susceptible to filiform corrosion, such as swimming pools.
Earlier studies initiated by GSB International have shown that filiform corrosion can only be prevented
with a preanodisation beyond the required warranty periods. This has in fact been confirmed in
outdoor weathering studies by the Forschungsgesellschaft für Pigmente und Lacke e. V. (FPL)
(Research Institute for Pigments and Paints), of Stuttgart, as well as by the Forschungsinstitut für
Edelmetalle und Metallchemie (FEM) (Research Institute for Precious Metals and Metallochemistry), of
Schwäbisch Gmünd.
Since 1995, the preanodisation layer, produced under defined conditions, has been certified by GSB
International as a pretreatment process for aluminium. It should be implemented in accordance with
the provisions of section 8.3 of the quality guidelines GSB AL 631.
Anodic oxide layers can be produced only on a metal connected as the anode, which is immersed in
an electrolyte. By the action of the electric current generated during the electrolysis at the anode,
atomic oxygen is liberated, which reacts with the aluminium, forming alumina. This is solidly anchored
to the metal surface. The layers consist of an impermeable barrier layer and a porous outer layer, the
achievable thickness and pore diameter of which depend on the current density, time, temperature
and acid concentration. The pore density is about one billion pores per mm2 of external surface.
To prepare the adhesive artificial oxide layer, sulphuric acid is generally used as the electrolyte. The
layer thickness can be adjusted via the process parameters of temperature, current density and time.
Highly suitable layer thicknesses have been found to range between 5 and 8 μm.
The following are considered to be the properties of the layer and the process:
Very good corrosion resistance
Variable adjustment of layer thicknesses
Special plant technology is required
Only achievable with dipping
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The anodic oxidation of aluminium, both in terms of the quality of the passive layers formed, and also
their technical importance, has a leading position in the surface pretreatment of aluminium. The very
good corrosion resistance, even under difficult operating conditions, and the good environmental
compatibility, are factors that favour the increasing use of these intermediate layers. The application of
preanodisation is a prerequisite for the awarding of the GSB International quality label "Sea Proof
Plus"
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8 Summary
Image: Requirements for chromate-containing and chromium-free surface pretreatments
Since its introduction 50 years ago, chromating has grown steadily into a safe process for the
pretreatment of aluminium. Only through this safe process technology could electrostatic powder
coating develop to include coloured forming of aluminium in the construction industry in the last
forty years, in addition to proven electrochemical oxidation.
In particular, the high process safety and high corrosion protection achieved are very highly prized
in the market.
The classification of chromium (VI) compounds as compounds with carcinogenic and mutagenic
potential has been known for many years. Therefore, their inclusion in the candidate list (SVHC
list) comes as no surprise to the affected industries.
The use of chromating for the pretreatment of aluminium, however, continues to be legally
permitted until a final decision by the European Commission is reached.
The relevant national building codes and rules, such as the REACH Regulation, also do not rule
out the application of this surface pretreatment process at the current time.
There is no absolute clarity regarding how chromium (III) compounds will be classified in the
future. This also includes green chromating, which still possesses a certification for coatings that
come into contact with food products. However, the production of process chemicals always starts
from the basis of chromium (VI) compounds.
68
It is important to note that it is already a requirement of some individual cities and districts that a
chromium-free pretreatment be enforced for the use of aluminium in public buildings. This raises
the question of what is actually to be understood by the term "chromium-free". This requirement is
not consistent with the national building codes and the REACH chemicals ordinance, and
represents a tightening of the requirements profile. Harmonisation and an unambiguous
interpretation would be in the interest of all parties involved.
Since 1994, chromium-free pretreatment processes have been certified for the coating of
aluminium according to GSB International guidelines QR AL 631. The market now has a wide
range of available choices of definitively certified processes.
Several million square metres of coated aluminium with chromium-free pretreatment are the hard
evidence of the process safety of this pretreatment process.
The chromium-free process used must be adapted to the production parameters of the respective
plants; and also vice versa.
A systematic and continuous bath monitoring of the chromium-free pretreatment is required.
According to the current state of the art, this is more challenging than in the case of chromating.
The health protection of employees is much more thoroughly guaranteed with the use of
chromium-free pretreatment processes.
The increased durability of chromium-free processes compared to chromating is an important
economic factor.
Preanodisation is the chromium-free process that offers the best corrosion protection and the
highest resistance to filiform corrosion. This chromium-free process has been used successfully
more than 20 years in regions with particularly aggressive climates.
According to the present results, chromium-free pretreatment processes are classified as being
comparable in their corrosion protection to chromating processes. There are studies that have
confirmed the higher filiform resistance of chromium-free processes compared to chromium-
containing processes.
Also in other industrial sectors, chromium-free pretreatment has now established itself. Chromium-
free pretreatment, despite the existing objections, results in increased sustainable protection of the
environment and humans.
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Acknowledgments
We would like to thank the fem, Forschungsinstitut Edelmetalle & Metallchemie, Schwäbisch Gmünd,
and all participating companies for their support, discussions, contributions and constructive co-
operation in the implementation of this document.
Legal notice: © GSB International 2012. Reprinting and photomechanical reproduction, even of individual pages of this work, is prohibited without permission. Translation of the 2nd, revised issue 2012. All rights, including translation into other languages, are reserved by GSB International. All statements, information and recommendations are based upon the information available at print time of printing and are provided without warranty or assumption of liability. Published by: GSB International e. V. Am Bonneshof 5 D-40474 Düsseldorf Tel.: +49 (0) 211 / 4796-450 Fax: +49 (0) 211 / 4796-410 E-mail: [email protected] Internet: www.gsb-international.de General processing: Hans-Jürgen Alfort, Dr. Axel Blecher, Werner Mader Title image: Hyatt Regency, Ekaterinburg, Russia (TK-Oberfläche, D-Bielefeld)